The present disclosure relates to vehicle restraint systems and more particularly to vehicle safety restraint pretensioning mechanisms which reduce slack in seat belts during impact.
With existing passenger vehicle restraint systems seat belts are provided with retractors which facilitate deployment and rewinding of the seat belt webbing in order to accommodate the individual using the system at any given time. Such retractors are also normally provided with locking features to lock the webbing based upon a predetermined operating parameter of either the seat belt webbing or the vehicle itself. For example, such systems will lock the webbing in the event of exceeding a predetermined acceleration of the belt or upon exceeding a predetermined rate of change in vehicle speed.
Another feature present in many vehicle restraint systems is a pretensioner mechanism. Such pretensioners commonly utilize a pyrotechnic device which detonates upon occurrence of predetermined parameters that define a triggering incident, e.g., impact of the vehicle with an object or another vehicle. Detonation of the pyrotechnic device initiates a rewinding of the seat belt webbing or a pull-down of the seat belt buckle a predetermined amount in the early stages of the triggering incident. This pretensioning of the seat belt webbing reduces the possible forward motion of an occupant during the triggering incident to reduce injury to the seat belt occupant which may otherwise result from impact with portions of the vehicle.
Upon detonation of the pyrotechnic device in such pretensioner mechanisms, extremely hot combustion gases are discharged to create the necessary pressure to drive a piston. A continuing need is always present for ways in which to reduce any undesirable side effects of these gases. For example, the scorching of any working parts which happen to be located in the flow path of the gases is such an undesirable side-effect.
In the past, seat belt pretensioning devices for buckles have been provided with wedges in attempts to maintain the pretension load. However, one disadvantage of such previous pretensioners is that they have been largely unsuccessful in maintaining a high percentage of the pretension load. These previous wedges were subject to unsatisfactory amounts of slippage in the strap system.
A need also exists for a pretensioning mechanism which effectively pretensions the seat belt webbing in the event of a triggering incident and which maintains a high percentage of the pretensioning load throughout the whole accident which triggered the pretensioner.